CEM3310 equivalent circuit
Moderators: Kent, luketeaford, Joe.
- oldcrow
- Super Deluxe Wiggler
- Posts: 1067
- Joined: Sun Nov 20, 2011 4:05 pm
- Location: Chicago, IL USA
- Contact:
CEM3310 equivalent circuit
Well, I have a working bread-boarded circuit. It uses JH's inverse-parallel exponential multipliers and traditional analog MUXing (and a 555 for peak threshold detection). Trying to make it compact enough to fit two of them on my Oberheim OBX voice card layout. Since the CEM3310 used tiny CVs with input dividers cutting -5V to -~50mV for time parameters, and the OBX CV storage buffers have inverting active attenuators to make this -50mV external to the CEM3310s, I have to use inverting amplifiers locally--not quite the traditional CV input scheme, but in order to avoid having to hack the OBX CV buffers to accept new voice cards this is the best solution. I guess I blame Doug Curtis for the negative-going time CVs, probably to save space in the interdesign chip array the 3310 was born from. ;) More later.
very cool! The oberheim OB-1 used these for the ADSR's on the later models and I've always _loved_ the envelopes on that synth, the reponse seemed very non-linear, without every actually checking it out I always assumed they were exponential rise and log decay... but your comments about the narrow cv range might actually have more to do with it, I remember the adjustment being oddly sensitive but at the same time very useful musically!
If you get this to work I've actually got a rough pcb layout done for the OB-1... a fantastic monosynth with full patch storage! Even better it actually interfaces with modern microcontroller setups very easily.. hmmmmm
If you get this to work I've actually got a rough pcb layout done for the OB-1... a fantastic monosynth with full patch storage! Even better it actually interfaces with modern microcontroller setups very easily.. hmmmmm

- negativspace
- Manhattan Analog
- Posts: 6574
- Joined: Tue Apr 13, 2010 2:50 am
- Location: Manhattan, KS, USA
- Contact:
Oh man, of all the synths I miss most it's the OB-1. Smoothest, most buttery low-end I ever had in the studio. I've been trying to reacquire one for years... this sounds interesting!moogah wrote: If you get this to work I've actually got a rough pcb layout done for the OB-1... a fantastic monosynth with full patch storage! Even better it actually interfaces with modern microcontroller setups very easily.. hmmmmm
(Sorry, that has nothing to do with the 3310.)
- filterstein
- Common Wiggler
- Posts: 63
- Joined: Sun May 13, 2012 3:35 pm
- Dave Kendall
- Set The Controls . . .
- Posts: 1275
- Joined: Thu Jul 16, 2009 7:20 am
- Location: England
moogah wrote:

Definitely be interested. Any more details Jeff?
Basic MIDI, eg. note in and PGM change to patch select would be awesome...
DIY and patch storage. Yumm. Very tempting....
cheers,
Dave
Now THAT is really something.....I've actually got a rough pcb layout done for the OB-1... a fantastic monosynth with full patch storage!

Definitely be interested. Any more details Jeff?
Basic MIDI, eg. note in and PGM change to patch select would be awesome...
DIY and patch storage. Yumm. Very tempting....

cheers,
Dave
Want to Buy: KURZWEIL KSP8
Want to Buy: old EFM PCBs
"Everything in moderation, including moderation"
Want to Buy: old EFM PCBs
"Everything in moderation, including moderation"
Apologies for the thread-jacking, but I suppose this is on topic enough 
Making an new OB-1 is something I could definitely pursue, but I don't think I'll be actively working on it until this fall in any case. My general plan is to create a voice pcb with a layout similar to the 9090 so that all off board connections are on headers organized at the edge of the PCB. A seperate control board can then be created which could either be just pure simple analog with pots or a full on digital setup.
The midibox hardware is already a perfect fit, literally using the same signal levels and multiplexers as the original
the apparent scarcity of the 3080 is a concern though, there are many of them in the circuit and I highly doubt it will really sound correct without them!
Another interesting note is how similar the OB-1 is to the SH-2 in design
.. I've got a layout in the works for that one too... but for real, I'm not trying to clone every old box out there LOL.

Making an new OB-1 is something I could definitely pursue, but I don't think I'll be actively working on it until this fall in any case. My general plan is to create a voice pcb with a layout similar to the 9090 so that all off board connections are on headers organized at the edge of the PCB. A seperate control board can then be created which could either be just pure simple analog with pots or a full on digital setup.
The midibox hardware is already a perfect fit, literally using the same signal levels and multiplexers as the original

the apparent scarcity of the 3080 is a concern though, there are many of them in the circuit and I highly doubt it will really sound correct without them!
Another interesting note is how similar the OB-1 is to the SH-2 in design

Scott,
Great news on a 3310 replacement!
Keep me posted as I would dearly love to have these for my own OB-X!
RE: OB-1
I repaired one of these once. Deemed unrepairable by at least two other techs. Found out one VCO had a bunch of transistors replaced with ones from a different manufacturer that were NOT pin compatible!
Very nice synth though! If they had poly'd that configuration, it would have been the ultimate Oberheim!
Tony
Great news on a 3310 replacement!

RE: OB-1
I repaired one of these once. Deemed unrepairable by at least two other techs. Found out one VCO had a bunch of transistors replaced with ones from a different manufacturer that were NOT pin compatible!
Very nice synth though! If they had poly'd that configuration, it would have been the ultimate Oberheim!

Tony
Great Lakes Modular
Design, Engineering, and Manufacturing services
Design, Engineering, and Manufacturing services
- Dave Kendall
- Set The Controls . . .
- Posts: 1275
- Joined: Thu Jul 16, 2009 7:20 am
- Location: England
Hope I'm not adding to the hijacking here
......
Out of interest, any particular MIDIbox project you were thinking of for control? I'm a bit behind with what uCapps is up to these days....
cheers,
Dave

According to This Link by its designer, the LM13600 is pretty much a straight cut and paste of two 3080s onto a single IC. There are some tiny differences between the 13600 and 13700, IIRC there has been some talk on the [sdiy] list about exactly what they are.the apparent scarcity of the 3080 is a concern though, there are many of them in the circuit and I highly doubt it will really sound correct without them
Out of interest, any particular MIDIbox project you were thinking of for control? I'm a bit behind with what uCapps is up to these days....
cheers,
Dave
Want to Buy: KURZWEIL KSP8
Want to Buy: old EFM PCBs
"Everything in moderation, including moderation"
Want to Buy: old EFM PCBs
"Everything in moderation, including moderation"
- oldcrow
- Super Deluxe Wiggler
- Posts: 1067
- Joined: Sun Nov 20, 2011 4:05 pm
- Location: Chicago, IL USA
- Contact:
Heya Tony,
Jurgen had this figured out 15 years ago, I just decided to add it to my "make an equivalent circuit" list after hearing MC's OBX and deciding I need to make enough of one to get that sound myself. More later.
Jurgen had this figured out 15 years ago, I just decided to add it to my "make an equivalent circuit" list after hearing MC's OBX and deciding I need to make enough of one to get that sound myself. More later.
glmodular wrote:Scott,
Great news on a 3310 replacement! :hail: Keep me posted as I would dearly love to have these for my own OB-X!
- oldcrow
- Super Deluxe Wiggler
- Posts: 1067
- Joined: Sun Nov 20, 2011 4:05 pm
- Location: Chicago, IL USA
- Contact:
For those interested, here is the CEM3310 equivalent circuit I am using in the OBX voice card. It is largely made from standard EG concepts, the only novel part is Jurgen's inverse-parallel expo multipliers as noted at
http://www.jhaible.com/tonline_stuff/hj_vc_hadsr.html
The 555 and 4052 are standard-issue in DIY EGs, Tom Gamble (EFM) and Thomas Henry are just a couple of names I recalled while breadboarding the circuit. The only extra trick I have to use is biasing the 4052's Vee pin slightly negative as the decay and release CVs are 0 to -250mV as per the CEM3310's time CV input spec, and 405x chips tend to latch up and explode if they see a voltage below a diode drop or so with respect to Vee for analog signals or Vdd for logic signals. Clamp diodes on the analog inputs are also used for this reason.
The 10-Ohm resistors are from the OBX voice card, probably something to do with trimming the maximum times that they never quite got around to. Since the OBX parameter CV storage buffers on their control board use inverting attenuators to take the 0 to +5V down to 0 to -250mV, I have to restore the full scale CV range using IC1, otherwise I would have to modify the OBX control board and for a drop-in voice card not particularly desirable. The trimmers are for figuring out the ideal resistors to actually use for the scaling--also taken from JH's HADSR.
--Crow

http://www.jhaible.com/tonline_stuff/hj_vc_hadsr.html
The 555 and 4052 are standard-issue in DIY EGs, Tom Gamble (EFM) and Thomas Henry are just a couple of names I recalled while breadboarding the circuit. The only extra trick I have to use is biasing the 4052's Vee pin slightly negative as the decay and release CVs are 0 to -250mV as per the CEM3310's time CV input spec, and 405x chips tend to latch up and explode if they see a voltage below a diode drop or so with respect to Vee for analog signals or Vdd for logic signals. Clamp diodes on the analog inputs are also used for this reason.
The 10-Ohm resistors are from the OBX voice card, probably something to do with trimming the maximum times that they never quite got around to. Since the OBX parameter CV storage buffers on their control board use inverting attenuators to take the 0 to +5V down to 0 to -250mV, I have to restore the full scale CV range using IC1, otherwise I would have to modify the OBX control board and for a drop-in voice card not particularly desirable. The trimmers are for figuring out the ideal resistors to actually use for the scaling--also taken from JH's HADSR.
--Crow

I'll be keeping my eyes open for any progress you make with the OB-1 clone later in the yearmoogah wrote:Apologies for the thread-jacking, but I suppose this is on topic enough
Making an new OB-1 is something I could definitely pursue, but I don't think I'll be actively working on it until this fall in any case. My general plan is to create a voice pcb with a layout similar to the 9090 so that all off board connections are on headers organized at the edge of the PCB. A seperate control board can then be created which could either be just pure simple analog with pots or a full on digital setup.
The midibox hardware is already a perfect fit, literally using the same signal levels and multiplexers as the original![]()
the apparent scarcity of the 3080 is a concern though, there are many of them in the circuit and I highly doubt it will really sound correct without them!
Another interesting note is how similar the OB-1 is to the SH-2 in design.. I've got a layout in the works for that one too... but for real, I'm not trying to clone every old box out there LOL.

- The Real MC
- Veteran Wiggler
- Posts: 691
- Joined: Sun Jun 02, 2013 8:36 pm
- Location: In front of computer
I don't think matching is necessary, they feed charging current to C1 which is where the transients are generated. Tempco errors (very small) only impact the A/D/R transients, and the human ear isn't as sensitive to shifts in timing transients as much as shifts in tuning.
I haz a wrench, to fix da synth.
http://www.analoguediehard.com/
http://www.analoguediehard.com/
-
- Learning to Wiggle
- Posts: 10
- Joined: Wed Nov 20, 2013 6:08 pm
- Location: Verona (ITALY)
Scott, your ADSR schematic is very similar to the one I developed in the 2004, see :
http://digilander.libero.it/ismsynth/vc-adsr-1.2.jpg
The core is the well known Jurgen Haible expo converter, but I got the idea of comparing the EG output with the capacitor asymptotic voltage and use the difference as a reference current for the expo.
I am currently trying to put the whole circuit in a small SMD module, not an exact CEM3310 replacement, but something small and useable as a building block for a polyphonic synth.
Bye
http://digilander.libero.it/ismsynth/vc-adsr-1.2.jpg
The core is the well known Jurgen Haible expo converter, but I got the idea of comparing the EG output with the capacitor asymptotic voltage and use the difference as a reference current for the expo.
I am currently trying to put the whole circuit in a small SMD module, not an exact CEM3310 replacement, but something small and useable as a building block for a polyphonic synth.
Bye
- oldcrow
- Super Deluxe Wiggler
- Posts: 1067
- Joined: Sun Nov 20, 2011 4:05 pm
- Location: Chicago, IL USA
- Contact:
Huh, interesting. If I'd seen this schematic six months ago it would have saved a bit of time.
I basically took JH's VC HADSR and reworked it with the traditional elements as used by Tom Gamble, Thomas Henry and possibly other guys named Tom.
I put it to good use: http://www.cs80.com/crowbx
--Crow
/**/


I put it to good use: http://www.cs80.com/crowbx
--Crow
/**/
Massimo Ischia wrote:Scott, your ADSR schematic is very similar to the one I developed in the 2004, see :
http://digilander.libero.it/ismsynth/vc-adsr-1.2.jpg
-
- Learning to Wiggle
- Posts: 10
- Joined: Wed Nov 20, 2013 6:08 pm
- Location: Verona (ITALY)
I prefer to work with IC rather than discrete transistors, so I prefer my and Scott schematics rather than the JH one.
Among other things, our solution is more clean (neat ?) and the operation is easier to understand (IMHO). The difference between my schematics and that of Scott is that my accepts control voltages between 0 and 5V (but it is preferable to place a buffer or use the output of an SH before the control inputs). Scott's one accepts negative voltages as for the CEM3310.
Among other things, our solution is more clean (neat ?) and the operation is easier to understand (IMHO). The difference between my schematics and that of Scott is that my accepts control voltages between 0 and 5V (but it is preferable to place a buffer or use the output of an SH before the control inputs). Scott's one accepts negative voltages as for the CEM3310.
- The Real MC
- Veteran Wiggler
- Posts: 691
- Joined: Sun Jun 02, 2013 8:36 pm
- Location: In front of computer
Actually if you remove the attenuator/inverter on the A/D/R lines then the circuit responds to 0-5V range. Scott added them so his CrOwBX voicecard would be drop-in compatible with vintage OBX. His schemo notes this:Massimo Ischia wrote:The difference between my schematics and that of Scott is that my accepts control voltages between 0 and 5V (but it is preferable to place a buffer or use the output of an SH before the control inputs). Scott's one accepts negative voltages as for the CEM3310.
oldcrow wrote:Updated from my crOwBX rev2 tweaks,
I haz a wrench, to fix da synth.
http://www.analoguediehard.com/
http://www.analoguediehard.com/
It's definitely cleaner and easier to follow. When I saw this my heart kind of sank a bit because I already did a board layout for the JH ADSR. I'm just about to order a whole batch of 16 boards and contemplating whether I should redo it with this implementation or just stick with what I have. But since it's done and works, probably not worth the extra effort at this point.
- Littlem4tt
- Common Wiggler
- Posts: 140
- Joined: Fri Mar 01, 2013 12:16 am